Many crustaceans (e.g., lobsters, shrimp, and crayfish) use their tails to swim, but crabs have reduced tails that curl under their shells and are not used in swimming. This is an example of _____.

Gill pouches in chick, human, and house-cat embryos are an example of _____.

Why does the pattern of resemblance between the fossil record and the living species in a geographic area support the theory of evolution by natural selection?
1) It provides evidence that species change over time.
2) It provides evidence of the law of succession.
3) It provides evidence that species become more complex over time.
4) It provides evidence of population thinking.

Why do related species share homologous traits?

Which is an example of a structural homology?
1) the similarity in number and arrangement of bones in vertebrate forelimbs
2) the same group of embryonic cells, which forms the adult jaw of a perch and a dog
3) the post-anal tail formed during vertebrate development
4) the common genetic code shared by all organisms

1) the similarity in number and arrangement of bones in vertebrate forelimbs

Fossils of Thrinaxodon, a species that lived during the Triassic period, have been found in both South Africa and Antarctica. Thrinaxodon had a reptile-like skeleton and laid eggs, but small depressions on the front of its skull suggest it had whiskers and, therefore, fur. Thrinaxodon may have been warm-blooded. Thrinaxodon shows _____.

Which of these conditions are always true of populations evolving due to natural selection?
Condition 1: The population must vary in traits that are heritable.
Condition 2: Some heritable traits must increase reproductive success.
Condition 3: Individuals pass on all traits they acquire during their lifetime.

How is biological fitness measured?

There is a population of beetles that typically have black wings. A scientist studying these beetles knows that their eggs hatch in early spring, the baby insects grow through the late spring and summer, they lay eggs in the early fall, and die in the early winter. Recently some beetles have been born with white wings. Early in life the black and white winged beetles seem to be very similar in number of mating events, eggs laid, and survival rates, but shortly after laying their eggs the white beetles die and there are only black winged beetles during the late fall. Which of the following is a true statement about the beetles?
1) Black winged beetles have a higher fitness than white winged beetles.
2) White and black winged beetles have equal fitness.
3) The number of baby white winged beetles will decrease in frequency over time.
4) White wings are an adaptation.

Cotton-topped tamarins are small primates with tufts of long white hair on their heads. While studying these creatures, you notice that males with longer hair get more opportunities to mate and father more offspring. You believe that having longer hair is adaptive to these males. You should _____.